1. Field of the Invention
This invention relates to end caps used for driving glass conveyor rolls made of ceramic.
2. Description of the Prior Art
Glass tempering and annealing furnaces conventionally include conveyors for carrying glass sheets during tempering and annealing of the glass. One type of conveyor utilized to carry the glass includes horizontally extending conveyor rolls of ceramic on which the heated glass sheets are supported. Rotary driving of the rolls conveys the glass over the rolls through a heating chamber of either a tempering furnace or an annealing lehr. One ceramic material utilized to form the rolls is a sintered fused silica that is made by grinding solid fused silica into small particles and then sintering these particles to each other at a temperature below the fusing temperature. Such a material is readily formed into an elongated shape of the rolls and has a relatively small coefficient of thermal expansion which is advantageous due to the extreme temperatures to which the rolls are subjected during use.
One conventional way for rotatably supporting and driving heated glass conveyor rolls of ceramic utilizes spaced bearings that support opposite ends of the rolls and a drive member having a toothed drive component such as a gear or a chain sprocket through which the roll is driven at one end of the roll. A metallic end cap is conventionally utilized to secure the drive gear or chain sprocket to the roll end. In another type of heated glass conveyor disclosed by U.S. Pat. No. 3,806,312 and subsequent U.S. Pat. Nos. 3,934,970 and 3,947,242, opposite ends of the conveyor rolls are supported and rotatably driven by continuous drive belts or chains in a frictional manner. Metallic end caps are also utilized with this type of conveyor roll to prevent wear at the ends of the roll where the frictional driving takes place.
Metallic end caps for use in driving ceramic rolls that convey heated glass have been conventionally secured to the roll ends in two different ways. A suitable adhesive bond between the roll end and the end cap has been utilized to some extent in providing the end cap securement. Heat shrinking the end cap onto the roll end has also been utilized in securing the end cap. In performing the latter securement, the end cap is heated to a very high temperature so that the diameter of a sleeve portion thereof increases prior to receiving the roll end and being cooled so as to heat shrink onto the roll end. In performing this heat shrinking securement, the internal diameter of the end cap sleeve portion and the diameter of the associated roll end must be closely matched so that the roll end is small enough to be inserted into the heated end cap sleeve portion but large enough to be securely clamped thereby after the cooling. Often, machining of the end cap sleeve portion and/or the roll must be performed in order to provide this matching. Roll ends with end caps heat shrunk thereon project outwardly from the glass furnace or annealing lehr to a location where the temperatures involved are not relatively high such that the end caps are not heated sufficiently to increase the diameter of their sleeve portions and loosen the clamping pressure that secures them to the roll. At the location where each cap sleeve portion terminates, the roll is subjected to the clamping pressure of the sleeve portion and has an adjacent portion which is free of this clamping pressure. At this location, the roll ends sometimes fracture due to the stresses involved.
While end caps for heated glass conveyor rolls of ceramic constructed according to this invention utilize helical spring coils with a construction that is hereinafter described, it should be noted that helical springs have been utilized with conveyor rolls heretofore as disclosed by U.S. Pat. Nos. 3,485,615, 3,485,618, 3,527,589, and 3,881,906.